Rol van Lesotho–Hooglandwater op Vaalrivieralge
Date
2013Author
Swanepoel, Annelie
Janse van Vuuren, Sanet
Van Zyl, Germarie
Metadata
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Long-term changes in the algal composition of the Vaal River, South Africa – did the Lesotho
Highlands Water Project play a role? The Vaal River has become so nutrient-enriched that
algal blooms pose problems. A unique opportunity arose to determine if there were changes
in the chemistry en algal composition of the Vaal River after oligomesotrophic Katse Dam
(Lesotho) water was imported to augment supplies in the light of growing water demands in
the Vaal River catchment area. Algal concentration and composition in the Vaal River during
three periods (between 1992 and 1994, 1998 and 2000, as well as 2004 and 2006) were compared
to those in the Katse Dam (1998–2006). Some algal species, initially absent from the Vaal River,
appeared in the river during and after transfer. Mixed algal assemblages found in the Vaal
River before transfer of Katse Dam water gradually changed after transfer to assemblages
mainly composed of cyanobacteria. The total algal concentration in the Vaal River Barrage
doubled from the period between 1992 and 1994 to that between 2004 and 2006, indicating that
the transfer of clear, oligomesotrophic Katse Dam water did not dilute the eutrophic Vaal River
water sufficiently in order to reduce algal concentrations. Results showed that continuous
downstream pollution and eutrophication of the Vaal River system eliminated the diluting
effect of Katse imports. This resulted in changes in algal composition and concentration in the
Vaal, characteristic of those associated with increasing eutrophication